1. Field of the Invention
This invention relates generally to friction stir welding. More specifically, the present invention addresses improvements in all aspects of friction stir welding of stainless steel and other materials that are harder than aluminum, wherein the improvements are focused on composite tools, control systems for friction stir welding machines, the use of fluids that can affect friction stir welding performance, modification of the hardness of friction stir welds, friction stir welding of pipe, the use of electric currents to affect the quality of friction stir welds, a mandrel for use in friction stir welding in pipes, improvements in friction stir welding of pipe, alternate spindle heads for use in friction stir welding, and consumable pin tools.
2. Description of Related Art
There are numerous areas of friction stir welding that can be improved because of the difficulties inherent in the process when dealing with metal matrix composites, ferrous alloys, non-ferrous alloys, and superalloys when using a superabrasive tool.
An example of an area in need of development is friction stir welding (FSW) in an underwater environment. Because FSW has such great potential for use with pipe, on-site use of FSW is going to be an important field of use. Specifically, drilling rigs operate in both saltwater and freshwater environments. Both types of water can affect FSW performance. It would be an improvement over the prior art to adapt to these specific and different underwater environments to improve overall FSW performance.
This aspect of underwater FSW relates generally to the issue of fluids that can be used to not only affect the cooling rate of an FSW weld, but the ability to alter microstructure of the resulting weld. Thus it would also be an improvement over the prior art to consider how various liquids and gases can be used to optimize FSW performance in order to improve the FSW process.
Another important aspect of the invention is directly related to the welding of arcuate materials. Specifically, FSW of pipe can be improved by various means and methods.
When dealing with pipe, the pipe itself can be altered to obtain an improved material for use in drilling applications. Specifically, when two pipes are joined on-site, there is typically a wide female end and a thinner and threaded male end. The male and female ends are coupled using the threaded screws to thereby create a longer length of pipe. It would be an improvement over the state of the art to alter the shape of the completed pipe such that it can be more easily inserted into the drill hole, and to optimize the size of a drill head for the resulting completed pipe.
Another aspect of FSW that has been developed pertains to the communications that are required between a control station and various remote spindle heads. While communication is obviously important, it is difficult when dealing with hazardous environments such as near a nuclear containment vessel. It would be an improvement over the prior art to provide an improved communications system for use in both hazardous and non-hazardous environments.